Why did jim implore his grandmother not to tell anyone about his injuries or how he received them

On the third night, Jim awakes to find Mr. Cutter trying to grope him. They get into a fight, with Mr. Cutter beating Jim fiercely about the face. Jim runs back home and in the morning feels disgusted, ashamed, and angry at Ántonia. He refuses to see her or a doctor and is worried about word getting around town. This is why he wants to keep it a secret.